Pleural Empyema

A 52-year-old man with diabetes presents with a 10-day history of fever, cough, and left-sided pleuritic chest pain despite 5 days of intravenous ceftriaxone for community-acquired pneumonia. Chest X-ray shows a left-sided pleural effusion. Thoracic ultrasound reveals the structure marked **A** — a loculated, multi-septated pleural fluid collection with internal echogenic debris. Thoracentesis yields purulent fluid with pH 7.10, glucose 35 mg/dL, and positive Gram stain for Gram-positive cocci. Which of the following best describes the pathophysiological stage of pleural disease and the most appropriate next management step?